Telegraph system



Oct. 4, 1938. w. w. cRAMl-:R

l TELEGRAPH SYSTEM Filed Oct. l0, 1936 4 Sheets-Sheet l o 8 om mv/A/VE/VTOR W WCRAMER A TToRA/EV Oct. 4, 1938. w. w. CRAMER TELEGRAPHSYSTEM Filed Oct. 10, 1936 4 sheets-sheet 2 R V RE E mM M NLA m VR T WmA Ww.,u W

Oct. 4, 1938. w. w. CRAMER TELEGRAPH SYSTEM 4 sheets-sheet s Filed 0G11.l0, 1936 www .www Mu HHHMWM m M+ l 0 L L NQ@ Hwnwnw HN IN1 m Hlll Mw wWW Oct. 4, 1938. w. w, CRAMER TELEGRAPH SYSTEM Filed Oct. l0, 1936 4Sheets-Sheet 4 /N VEN Tof? W W CRA MER A from/Ey vPatented ct. 4, 1938UNITED STATES j A j V2,131,8711 TELEGRAPHSYSTEM i Walter W. Cramer,Rutherford, N.

J., assignor to Bell TelephoneLaboratories, Incorporated,l New York, N.Y., incorporation ofNew York .Application october 1o193s,scra1`Nc.164,959

This invention relates to telegraph systems and more particularly t'oimproved arrangements `for transmittingtelegraph signal impulsesover'long open-wire telegraph lines and over the telegraph channels oflong open-wire toll lines.

Long open-Wire lines of thesev types are subjected to varying weatherconditions. This causes a varying leakage resistance Vwhich varies overwide limits from a very high value under dry conditions to a relativelylow value under wet weather conditions. Both` the duplex and upsetduplex telegraph transmitting and receiving arrangements usuallyemployed at the ends -of long lines of this type'must be adjusted toCompensate for this variation in the leakage current of the line inorder to insure the correct reception ofthe telegraph signals. Variationof the leakage of the line `tends to cause aV variation'in the bias ofthe received signals which must be compensated for by `a variation ofthe biasing current of the receiving relays at each end of the line.This adjustment must be made in accordance with the variations in the'leakage of the line so that it is necessary, at times, to adjust thisbias current at the ends'of the line at rather frequent intervals, thuscausing a high cost of circuit maintenance. This is particularly true inthe case of an outlying subscriber Where it is very difficult ltoprovide suitable maintenance of the telegraph circuit because thesubscriber is soi far removed from the telegraph station vor repeaterpoint, as is the usual case when transmitting telei graph signals overlong circuits of this type.

It is an object off this invention to greatly re- Y duce the amount ofmaintenance and adjustment required, rst, at the outlying or subscribersend of the lineV and, second, at both ends of the line withoutintroducing any biasing or other distortion of the telegraph signalsfrom any other source. Y

In accordance with one embodiment of this invention the outlyingsubscriber or telegraph station is arranged to be self-compensating orto require no balancing with changes in the leakage or leakageresistance of theline connectingv that station to the central station.This arrangement, however, requires additional maintenance andadjustment of the biasing current and balance at the central stationbecause the signals received at the central station vary more withleakage than do signals received from the usual duplex arrangementswhich require balancing at bot ends of the line. In accordance withanother embodiment of this invention; however,I after the central oiiice29 claims. (ci. 17u59) end has been adjusted to correctly receive thesignal impulses, Vthe adjustments atboth ends of the line need not bealtered with changes in leakageolf the. line because thesignal impulsesarriving thereat will cooperate with the receiving apparatus to producesignal impulses substantially unaffected by variations in the leakageof` the line. In 'other' words, the circuit is arrangedto fully andautomatically compensate for changes in the Aleakage resistance of theline. A Itis `also within the scope of this invention to combine linesections of' the two` above arrangements and to combine either one withexisting typesof line Sections in suitable comprehensive telegraphcommunication networks. Within the Scope'of this invention to modify andadapt these arrangements to operate satisfac- It is also l,

to-rilyV with various types of telegraph equipment and vario-us `typesof telegraph circuits.

While the vnovel features of this invention are specifically set forthin the claims Vappended thereto, the foregoing and other objects andfeatures fof `the invention may be more readily and more-'fullyunderstood from the following descriptionwhe'n readA with reference tothe'attached drawings in which:

Fig. 1 illustrates an embodiment of this invention requiring adjustmentat only one end of the line'tocompensate for changes or variations inthel'eakagc of the line; Fig 2 shows an embodiment of the inventionViivhi'ch'requires no change in adjustment at either endof the line tocompensate for variations in the leakage of the line;

Figs. B-A YtoY 3-C, inclusive, illustrate the various signalingconditions normally encounter'- ed in the system shown in Fig. 2;

. Figs; ihA to Ll-F, inclusive, illustrate in diagrammatic form themanner in which the various currents received from the telegraph linevary with leakage under various conditions;

Fig. 5 shows the manner in which Figs. 6, 7 and 8 are arranged to form atypical comprehensive system to which this invention is applicable; andY Figs. 6, 7 `and 8 when arranged as shown in Fig. 5 show acomprehensive telegraph system embodying features -ofathe systems shownin Figs. 1 and v2-1nodiiied and adapted for use with different telegraphcircuits. Referring now to Fig. 4l, A represents the iirst telegraphstation and B the-second telegraph station `.which areconnected bytelegraph line I0. Telegraph line I0 may be of any suitable directcurrent telegraph Vline or channel and may include or comprise atelegraph leg of a composited long distance toll line in which case itwill include terminal composite sets as well as intermediate compositesets. In addition, various sec'- tions of the line may include entrancecable and open-wire lines. Various sections of the line may also besimplex lines and other sections may be straight direct currenttelegraphl lines. The open-wire sections of said line I0 are subject t0varying leakage due to changes inthe weather conditions. sistance of theline is very high and usually may be neglected. However, during wetweather the leakage resistance of the line falls to a relatively lowvalue which seriously interferes with the transmission of telegraphsignal impulses over the line unless compensating changes are made.'

However, in accordance with Fig..1.the terminal equipment is so arrangedthat no compensation for changes in the leakage of the line need to bemade at station B. At. statiorrB the line I0 is normally connected toground through vthe sending contacts II of a suitable transmittingdevice such as for example the transmitting contacts of ateletypewriter` shown in Fig. 1. At station A telegraph signal impulsesare transmitted from the contacts of the sending relay I2. The markingand spacing contactsof relay I2 are connected to two substantially equalsources of potential or batteries I3 and I4 of negative and positivepolarity, respectively. These signals are transmitted over line III andactuate the receiving relay I5 at station B. Any leakage of the line toground will affect both the positive and negative signal impulses orcurrents equally. Consequently, on arriving at station B these currentswill operate the receiving relay I5 equally fast in both directions andwill not therefore affect the bias of relay I5. In other words, thealgebraic sum of these currents is constant. Since relay I5 is a polarrelay and receives equal positive and negative current, it may be givena zero bias. In other words, it will operate as wellv and as, fast inone direction on positive current as it will operate in the oppositedirection on negative current. Consequently, when this relay is soadjusted and receives positive and negative signal impulses from thecontacts of relay I2, the response of relay I5 will be substantiallyindependent of the leakage in line I0. This condition is furtherillustrated in Fig. 4-A which shows in diagrammatic form the currentreceived by relay I5 as the leakage of the line decreases from innity tozero. Itis to be noted that the marking current received by relay I5 asshown by curve M,of Fig. 4-A increases just as much as the spacingcurrent receiv-ed by relay I5 at station B decreases as the leakageresistance of the line decreases. It is to be understood that the curvesin Fig. 4 are to illustrate this feature and that the scale of theleakage resistance has not been shown. Such a scale of leakageresistance is assumed as will make the curves M and S be straight lines.In actual practice if the scale of the leakage is linear, curves S and Mwill not be straight lines but curved lines which will approach the zerocurrent condition asymptotically as the leakage resistance approacheszero. However, as-shown in Fig. 4-A at any given value of leakage themarking current received by relay I5 has the same magnitude as thespacing current received by relay I5. Consequently, relay I5 willrespond to both marking and spacing current Without any addition of biasto the signal.

The term bias as applied to signals indicates During dry weather theleakage rea lengthening of one signal impulse and a shortening of theother signal impulse. For example, marking bias means that the markingsignal impulses are lengthened and the spacing impulses shortened,whereas spacing bias means that the spacing signals are lengthened andthe marking signals are shortened. Thus the greater the bias of thesignals the less satisfactory they are for operating telegraph apparatusor the poorer in quality they are, while the less the bias the better`the quality of the signals.

A common cause for this lengthening and shortening of the varioussignals is that the marking and spacing currents are unequal, forexample, for marking biasthe marking current is greater than the spacingcurrent whereas for spacing bias the spacing current is greater than themarking current. However, as pointed out above with the arrangementshown in Fig. l, the receiving device I5 at station B receives equalmarking and spacing current and consequently does not introduce any biasin the received signal and requires no biasing winding tocompensate forany such bias. The terms marking and spacing as used in thisapplicationv'diierentiate the two line or signaling conditionstransmitted between telegraph stations. The term marking is used todesignate the line or'signaling condition employed during the time nosignal impulses are being transmitted but the system Vis energized andready totransmit signal impulses. The term spacing designates othersignal or line condition.

Referring again to Fig. 1, ytransmission from station B is effected bythe opening and closing of the contacting device II in accordance withthe signal impulses to be transmitted. During the open periods of thesecontacts battery I6 is connected through resistance Il to the line II).The potential of battery I5 is of the same polarity as the source ofpotential I3 normally connected to the telegraph line at station A.However, the source of potential I6 is of a greater magnitude than thesource of potential I3 or the potential of point 23 so that itoverpowers the potential source I3 and causes current to ilow in thereverse direction over line I0. If, as in the preferred embodiment,source I6 is twice the magnitude of source I3, or rather the potentialof point 23, then the two line .currents will be of equal magnitude`lout opposite polarity. Under these conditions the receiving relay I8would require no additional biasing or balancing winding. However, sincea balancingwinding I9 is provided, a biasing winding 2l] must also beprovided to compensate for the direct current flowing in winding I9 toinsure proper operation of the receiving relay I8. The balancing windingI9 and balancing network 2I are required to prevent the operation orrelay I8 during the transmission of signal impulses from the sendingrelay I2 over line I to station B. If there were no leakage ori-theline,'current through the biasing winding 20 could be adjusted once bymeans of resistance 22 and thereafter remain constant.

However, in case a variable lead due to varying weather conditions isencountered in line I0, it will be necessary to alter the adjustment ofthe biasing current by varying resistance 22 to compensate for variationin the leakageV current. Fig. 4-B shows the manner in which the markingand spacing currents received at station A from station B vary withvariations of the leakageresistance of line III.r In order to compensatefor variations` of the leakage resistance it is necessary to adjust thebias of the receiving relay |8 along line 89 of Fig. l-B. It is alsopossible to control the'potential of point -23 by varying the-resistance24 and thereby also eiiect the compensation `forthe variation of theleakage ofV the line. It should be noted that the values of both thepositive and negative potentials applied to line ||l are varied byresistance 24,` thus insuring that the bias of the signals received bythe receiving relay |-5 at station B will be unaffected by the Avalue ofthe leakage resistance of the line. i

Coils25, 26 and elements 21, 28 and 29 are provided tok reduce thenoisein aI telephone circuit due to the operation of the transmitting devicesat the respective telegraph stations and also `to properly adjustlandcontrol the magnitude of the line current flowing in line I0. Itis to beunderstood that anysuitable filter arrangement may beused in place ofthe coils 25 and 2B to reduce noise in the telephone circuit. Inaddition this noise reducing arrangement maybe omitted in case the lineis not composited and transmits only direct current telegraph signalimpulses. l* w At station B printer magnet Y3|.' is connected to thecontacts of the receiving relay l5. A compensating resistance 3| isalso-connected to these contacts. The compensating resistance '3| isprovided to maintaina load on sourcelE-, `which is the same as thesource 32, so that substantially constant potential is applied to theprinter magnet and line I during the operation of receiving relay l5.When the relay moves to its'opposite or spacing conta-ct it interruptsthe circuit of magnet 3|), thus decreasing the load on source I5. Thepotential of source I6 will then tend to increase. To prevent thisresistance'Sl is connected to the source 32 which is the same as I6 andprovidesa compensating load to maintain the voltage thereofsubstantiallyconstant. In addition, when contacts Il open duringtransmission of signal impulses, relay l moves to its opposite contact.This reduces the impedance between the line and the source of potentialshown as |6 and 32. Resistance 3| serves, under this condition, toreduce this impedance and maintain it ata low value and thus tends toimprove the transmission from station B. This resistance `is moreessential in case the load carrying capacity of this source ofpotential, which may be a rectifier or small motor generator, is justabout adequate to supply the load.

Elements 33 provide contact protection for the contacts of receivingrelay |5. Y

Sending relay |2 and receiving relay |8 may receive signals from andtransmit signals to other relays of other types of suitable telegraphrepeaters, as, for example, duplex telegraph repeaters, Vvoice frequencycarrier current telegraph repeaters, carrier current telegraphrepeaters, etc., as Well as from subscribers lines. In addition sendingcontacts may be replaced by sending relay contacts actuated by anothersubscribers line. In this case the contacts of relay |5` would transmittoV the subscribers line. In the embodiment of this invention shown inFig. 2, the terminal circuits of line |0'are arranged to transmit andreceive telegraph signal impulses so that the received signal impulsesat both ends of the line will be substantially independent of variationsin a leakage of the line'.

For the purpose of illustration, it will be first assumed that theleakage resistance of the line is concentrated at a single point and isrepresented' byA leakage resistanceRa inY Fig. 2 connected to line..lll. The resistance of line I0 is represented by resistance R1 and R2,which also include the resistance of theterminal apparatus connected tothe respective ends of -line I0. As in Fig. 1, it is to be understoodthat line il may comprise any suitable direct current telegraph channel,including the telegraph channel of a composite-toll line, inwhich casethe line may include both terminal and `intermediate composite sets. Inaddition, line |l may include portions of cable circuits includingentrance cables commonly employed in open-wire lines, where these linespass through cities and towns. As in Fig. 1, the line at station B isnormally connected to ground through the contacts oa sending relay 38.Signals are transmitted from station A to station B by means of sendingrelay 2 which may be actuated by signal impulses received fromanysuitable source, including various types of telegraph repeaters.Relay |2htransmits the corresponding signal impulses or currents byconnecting the positive and negative sourcesof potentials i4 and i3,respectively, to the telegraph line Ill. These sources ofV potential areof `substantially equal magnitude so that substantially equal currentsof opposite polarity will be transmitted over line IE! in accordancewith the `operation of relay |2. These currents will be equallyattenuated by the line and the leakage resistance and will havesubstantially the same value when received by relay l5 at station B.Receiving relay l5 at station B is provided with substantially no or`Zero bias so that receiving relay I5 will respond equally well to bothof the signaling currents received thereby and will, consequently,introduce 4no bias distortion as described in connection with Fig.V land shown inlig. l-A. f

In order to more readily understand the opera- `tionfof the transmissionof the signals in the reverse direction from station B to station A,referencewill be made to Figs. B-Ato 3-C`, inclusive, which-illustratethe various signaling conditions.

. Fig. 3-A illustrates the connections to line |0 when .both stationsare normal or transmitting marking signal impulses. ,.li'ig. S-B showsthe conditions when station A is transmittinga spacing impulse tostation B. As may be readilyseen from these gures, the positive currenttransmitted to station B under these conditions will be attenuatedsubstantially the same amount as the negative current from station Aunder marking conditions. Consequently, the algebraic sum of. these twocurrents, as received at station B, will be independent of the leakageresistance Rs of line lll because the sum will always be zero.

Fig. S-C shows the circuit connections during the time a spacingimpulseis being transmitted from station B to station A and if the receivingdevice at station A is torespond to this spacing impulse as readily asit does to the marking impulse, when the line lil is connected to groundas shown inr Fig. S-A, it will be necessary for the algebraic sum ofVthe currents received at station A to be independent'oi the leakageresistance Raof the line. It will be also necessary to adjustthemagntude of the bias of the receiving relay i8' at station A tothe'average of these two currents to insure proper operation which isinderent i1 received at station A during the transmission of markingimpulses from station B, as illustrated in Fig. 3-A, is as follows:

Rz'Ra R1+R2+R3 and the current i2 received at station A during the timethe spacing impulse is being transmitted from station B is as follows:

E2R3 i2 E- 1+ RH- R3 Rz-Rs R1+R2+Ra The sum S of these currents i1 andi2 is E2-R3 2E1+R2+R3 Rz'Rs R1+122+R3 As pointed out above, if thesignals received from station B are to be substantially independent ofthe line leakage resistance R3, it is essential that the sum of thesetwo currents shall be independent of the value of the leakage resistanceR3 or dS fr Diiferentiating the sum S with respect to R3, equating it toZero, and simplifying, the condition required for the sum S to beindependent of the value of R3 is as follows:

Thus we see that by controlling the relative magnitude of the potentialsat each end of the line with respect to the location of the leakageresistance along the line, it is possible to maintain the algebraic sumof the marking and spacing currents as received at station Asubstantially independent of the value of the line leakage resistance.

In the above example, it was assumed that the line leakage resistance R3Was concentrated at a denite point along line I0. In practice, however,this leakage resistance is usually distributed along the line or alongsome portion of the line. If the exposed portion of the line whichexperiences the variation of line leakage is somewhere near the centerof the line,rthe line leakage may be replaced by a concentratedeffective line leakage resistance which is at the center of the exposedline and the potentials at the ends of the line adjusted in accordancewith the position of this concentrated effective leakage resistance R3.In case the line is substantially all open-wire line and all, therefore,subjected to varying distributed leakage throughout its length, theconcentrated eiective resistance may not be at the center of the line.It has been discovered that if the terminal impedance of the receivingand transmitting devices connected'to the line is very low, thedistributed leakage of the line I0 may be replaced by a concentratedeffective leakage resistance which is located approximately 0.4 of theresistance of the line from station A. If the terminal resistance of theline is relatively high, then thc distributed leakage of the line shouldbe replaced by an effective resistance which is substantially at thecenter of the line between stations A and B. In practice, the positionof the equivalent concentrated Vresistance is usually between about 0.45and 0.5 of the resistance of the line from station A.

The action of the circuit during the transmission of signal impulsesfrom station B to station A may be also explained by reference to Fig.L.l-C. In this gure the line marked M represents the variation in themarking current received at station A during the time a marking impulseis transmitted from station B by sending relay 38 connecting ground toline I0 over an obvious circuit. Similarly, curve S illustrates themanner in which the current received at station A varies with theleakage resistance of the line during the times spacing impulses aretransmitted from station B by relay 38 connecting the source of positivepotential 93 to line I0. It is to be noted that as the marking currentincreases the spacing current decreases a corresponding amount so thatthe sum of the currents is substantially constant. By providing abiasing current for the receiving relay at station A which is equal inmagnitude but opposite in direction to the average of these two currentsrepresented by line I3 of Fig. 4-C, the resultant magnetic eiect oithese two currents upon the received relay I8 will be substantiallyequal under all conditions of line leakage. Thus, the response to thereceiving relay at station A is also independent oi the line leakageresistance R3.

It should be noted that during spacing signal impulses transmitted fromstation B to station A of Fig. 2, the line current is increased becausethe source of potential 93 at station B aids the source of potential I3connected to the line at station A. This is just the opposite from thearrangement shown in Fig. l in which the source of potential I6connected to the line at station B opposes the potential I3 normallyconnected to the line at station A. In the usual telegraphic circuit,resistances R1 and R2 are approximately equal so that the magnitude ofthe source of potential I6 should be approximately twice the magnitudeof the source of potential I 3. Under these conditions the line currentis increased to about three times its normal Value when a spacing signalis transmitted from station B to station A. When resistances R1 and R2are approximately equal, substantially equal powers or currents arereceived by the receiving relays at both ends o1" the line. This meansthat the relays at each end of the line should be of the samesensitivity and that the length of the line is not limited by theapparatus or relays at one end more than by the equipment at the otherend of the line.

In order to readily adjust the effective values of these potentials, avariable resistance 24 is connected between the armature of the sendingrelay I2 and line I0, as shown in Fig. 2. rIihis variable resistancepermits the potential of point 23, which is the effective potentialapplied to line IIJ, to be varied because resistance 24, in combinationwith resistance 29, the resistance of the balancing windings of relaysI8, 34, 35, and the resistance of balancing network 2i, form apotentiometer. Thus, by varying the resistance 24, it is possible tovary the potential of point 23 and thus adjust the effective value ofthe potential applied to line Ill at station A. It should be noted thatwith this arrangement, the values of both the positive and negativepotentials applied to line I0 are simultaneously varied, so that theyare both of substantially the same magnitude and thus transmit currentsof substantially the same magnitude to station B independently of thevalue of resistance 24, thus insuring that the bias of alloreceivinglrelay I at station B will .be unaffected by Variations 91"the;.1a.kagez l." esistane 0f @913155 As shown in Eig. 2, the particularsystem i'sv adaptedfor `use in a telegraphic system in which an averageuof `the twoline conditions `received from stationB. It isto beunderstood thatthese relays may be provided. additionfal.,vs'liruiings-, .l Y 1 bythe usual vibrator ywindings connected intheusualvibratorfcircuit and con-` Y as, for example,

`milled by the vibrating relay V35.11;@@sito `be understood that `asimilar arrangement may also-l be provided, at station Av of 1.`,Howeven under certain conditions, i as, for exarnple,` with relativelyshort lines, the vibrating relay maynot,`

be required. .t y. Y* t f t l l Since no bias orv zero biasis requiredfor. the; receiving relay l5 at station B, the balancing network 36,connectedto the balancing; Winding `3'I of relaylj, `isprovided tobalance onlyY the `alter- `hating-current componentspi the telegraphsig-V .nals transmitted over line `I t). With this arrange-f.

ment the auxiliary bias Vwindings shown-on the relays at station `A :areeliminated. It `is-.to be understood that a similar arrangement'of thereceiving relay may be employed at station `B` in the arrangementvshownin Fig-V. l. The arrangement shown :inFigtvZl has `a further advantagein that the received telegraph" signal impulses and` particularly thehigher frequency alternating-c11r` rent components.ofA these receivedsignal impulses do notl need to pass through the `high inductance ofelement 2t of the transmitting noise vlter.

' The printing magnetv or :relay 3Q of Fig.-2 .is arranged toreceive,polar signalV impulses from ref ceivingrelay. I5. One terminalY ofthegwinding of relayrisconnectedto the armature of relay I5, while theother `terminal `of the windingof relay 3E) is `connected toaboutthemid-point of potentiometer comprising resistances 46 so .that thismid-point issubstantially'at half the'poten-v tial of source 93..Ihe'marking and spacing. con-V tacts of relay I 5 are connected toground through marking contacts of thefsrending relay 38 `and-tc battery39 through the rupper winding `of-.the

break relay 4I, respectively. `Thus when receiveY ing relay I5 is; onone contact, current :flows from the mid-pointv of potentiometer`comprising` resistances throughthewinding of relay ormagnet 30 toground and when relayQ-I 5 is onits other contact, current flows` in the,opposite direction through `the windingof relay Gr :magnet- I5 frombattery through the contacts of relay I5.l to the mid-.point ofpotentiometer` llt.A f

Break relay 4I isprovided to insuratheY inten# ruption or, the home copyof the `teletypewriter machine at,stationBduring,the reception V-ofzabreak: signal over line it?. Thishrelaylisonly re-V quired forteletypewriters which are not provided with a break lock.l `In addition,relay 43` is provided to normally connecttherline I0, toground throughresistance Il'l'during thei'time the appa ratus at station'Bis lshutdown and the power supply 'disconnected It is to be understood thatadditional `telerypa writer apparatus may be connected in `series withvthe teletypewriterapparatusfshown atV station B. For example, additionaltransmitting contacts IImay be connected in seriesrwith Vthe transmi-Ladditional `receiving relays or magnets 3i? may be connected-in seriesWith'th'e magnet M30 shown in Fig. 2, providing additional localtelegraph transmittingtandreceivingstations; anyone of which may.transmit messages to' all of theothers and over vline I,as` wellasreceive messages from line I Il.;V Furthermoregthe` .transmitting andreceivinglapparatusfcohnected to both ends cf the line maybe" part ofrepeaters'connected to any type of,v Llegr'iph linesandapparatus su'chasto subscribfr'slinescomposited toll lines, carrier curfait` 1ines,.etc.i,t v l ',.A compensating Altiadl is` connected to the contacts of theVceivingvrelayf I5 and the source oipotential' 4l) to lprovidefa moreconstant load andthus a more constant Vsource of potential,

thus insuring moreuniform ,operation of the circuitfarrangement duringlthe transmission of sig-` n'al irnpul'sesjbyfrelay 38j.,` Thisvcompensating resistarjice'-3l isparticularly desirable when the sourcesof potential 16,33 and '4t are provided by a rectifier or motor`generator of small power Capacity. t l

. 4IrlV adjusting "the circuitV arrangement shown in Fig. YZgit, is`usually`, desirab1e to provide asource ofpdtential'BS abouttwice asYgreat as the sources of potential v,I3 .and I4, and vto make minor adiiustinehts'ifthe'effective potential transmitted to line tIfllfronistation A byfvarying the value of advantage thatpallfthe adjustments maybe made aton en'dlofjthe line; preferably at the central, inter nnectingor branch point or station shown as statior1 ,A,i`rl Fig. 2.j 1

M`fI,ria's'muchas.thepowenreceived by the receiv- V ingrelays `aticachof the stations is less during wet"weathe`r ,ortimes oflow leakageresistance;

is usually Vdesirable to adjust resistance 24 and alsothe resistance 22of the biasing circuits of the receiving relays at station A at thistime so as tojinsure'proper operation` of these relays. Thenfwhen theLleakagefresistance R5 increases duringthe dry Weather," the poweravailable to operate the relays increases and the'adjustments are not socritical." However, the magnitudes of `both the marking and spacingcurrents increase biaspf receiving relays is to adjust the biasingcurrentowing through the biasing windings, as

` forexample, by adjusting the values of resistance 2 2. atfstation-AjofFigi. 2. This has the effect vof raisingor lowering thevbias line shownin Figs. 1 Aj to` Lf-F.Y ;InFig. ,4f-D, this condition is il lustratedwhere the bias line 45 is shown raised. Under. these conditions', itshould be noted that the-spacing current crosses the biasline in someposition valongthe line, depending upon the amount `thebiasis varied.IThis means that as the leakage current varies, the biasing currentthrough the relaysmust also be varied to provide the same amount ofbiastot the signals received thereby vand transmitted from its contacts.However, by also varying the resistance 24 at station vA it is possibleto raise orlower the apparent intersection ofthe-marking and spacingcurves, as

`shown in Figefi-,IEi so that they will intersect on resistance. L Thisarrangement has the further the new bias line 44 as shown in Fig. 1 -E.When this is done, the amount of bias addedjto the signals by thebiasing current flowing through the biasing windings is more nearlyindependent of the value of the leakage resistance R3 and consequentlywill require much less adjustment as the leakage resistance of the linevaries.

As pointed out above, the curves shown in Figs. fl-A to 4-F are shown asintersecting straight lines merely to illustrate the relative manner inwhich these two currents vary, it being understood that the leakagescale is not linear but is so proportioned that the marking and spacingcurves M and S are straight lines. If the leakage scale were linear,then the lines M and S would be curved and .approach the bias lines asasyxnpf totes.

It is to be noted that the transmitting impedance of transmittingapparatus at both ends of line Il) in both Figs. 1 and 2 issubstantiallythe same during the transmission of both signalingconditions. Thus the cable capacity will be charged and dischargedequally under both signaling conditions when either of the two stationsis transmitting. Consequently, no distortion will be introduced fromthis source in the arrangements shown in Figs. l and 2. In Fig. 2 themarking contact of relay 38 is connected directly to ground while thespacing contact is connected to a source of positive potential 93through a protective resistance 92. Resistance 92 is usually so small,however, that the impedance as seen from the line is substantially thesame when relay I5 is on either contact. Likewise contacts I I. of Fig.1 are connected directly to ground, while line I0 is connected tosources I6 and 32 through additional resistances when these contacts areopen. These additional impedances or `resistances should be as small aspossible without placing too great a load on the power supply. Inpractice the impedance to ground is substantially constant under bothsignaling conditions so thatV it is only necessary to make very slightbias adjustments at the other end of line Ill (station A) to compenflsate for these different impedances.`

While only single line sections have been shown in Figs. l and 2, it isto be understood that these embodiments of the invention may be modiedand adapted to i-lt into comprehensive telegraph systems connecting anumber of stations over both single section and multisection lines. Atypical system of this type is illustrated in Figs. 6, 7 and 8 whenarranged in accordance with Fig. 5. The system shown in these figures isdesigned to provide communication between the outlying subscribers ortelegraph stations 49, 50, 5I, 52 and 53 by means of line sectionsin'accordance with this invention. Fig. 7 shows a more or less centralconnecting or branch station or point. 'Ihe apparatus shown in Fig. 7will usually be located in one central oflice orinterconnecting'station. However, it is to be understood that this neednot necessarily be so because each one of the repeaters shown in thisgure may be located at a Vdifferent point and still be connectedtogether by telegraph lines to provide satisfactory communicationbetween the various outlying telegraph stations.

The subscribers or outlying telegraph stations 49, 5G and 5I areconnected to the central point by means of circuit arrangements inaccordance with Fig. 1. However, inthe case of stations v50 and 5I anadditional outlying station close to the other station is shownconnected to the same line to the central station. In this case, insteadof connecting ground to the common terminal of the transmitting device II located at station 5I, a line is extended from this common connectionof the contact device II at station 5I over a short local telegraph line54 to a second station 50. The circuit arrangement at station 50 issomewhat modied from that shown at station 5I of Fig. 6 and at B in Fig.1 in that the printing magnet of a printing telegraph machine or otherreceiving device 30 is shown connected directly to the contacts of thereceiving relay I5 and is not connected in the circuit of source ofpotential I6 and resistance I1. Either arrangement works equally well.However, the arrangement shown at 50 requires slightly more power thanthe arrangement shownlat station 5I of Fig. 6 and station B of Fig. 1.It should also be noted that the source of power at station 5I is shownto be a rectifier and it is to be understood that the power supplied atany of these stations which are illustrated by either batteries orrectiers in the various gures of the drawings, may be rectiers,batteries, motor generator sets, or other suitable sources o directcurrent power. In addition, it is essential in the case of the rectifier55 shown at station 5I that the direct current side be ungrounded andinsulated conductively from the alternating-current power supply 56connected to the rectier.

As in Fig. 1 the line from the receiving relay I5 passes throughelements 26 and 21 to reduce the noise of the telegraph signals intelephone circuits in case the line passes over a composited telephoneand telegraph line. In addition, the line I0 extends to the repeater 51at a distant point. The lineV side of the repeater 51 is similar to thearrangement shown at station A of Fig. l` The receiving relay isprovided with a line winding, balancing winding and a biasing winding.In addition, the sending relay 58 connects negative and positive batteryto the line through the noise lters or filtering element 25 andresistance 24. 'I'he telegraph line at the subscribers station yisnormally connected to ground so that the positive and negative signalimpulses transmitted from repeater 51 to both telegraph stations 5I and52 are equally attenuated. Consequently, receiving relays I5 at thesestations when adjusted to have Zero bias respond equally well to bothtypes of signal impulses independent of the leakage resistance of theline I0. The spacing signal impulses transmitted from stations 50 and 5Ito the repeater51, however, connect the source of potential 55 orbattery I6 to line I0. The sources of potential 55 and battery I6 areabout twice the magnitude of the sources of potential I3 and I4 ofrepeater 51 shown in Fig. 7. This causes the line current to reverseduring spacing impulses transmitted from stations 50 and 5I to repeater51. However, as pointed out above in case of line leakage, variations inthe bias of the receiving relay I8 of repeater 51 shown in Fig. 7 mustbe adjusted to compensate for the different line leakage resistances asshown in Fig. Ll-B. The local side of the repeater 51 is provided with asending relay 58 and a break relay 59 which are in turn connectedthrough a single line repeater 60 to other repeaters as shown on Fig. 7.Repeater 6l) may be located at the same point as repeater 51 or may beconnected thereto by means of `a short telegraph line or conductor 6I.It is to be understood, however, that the length of this line 6 I, alsothe length of line 54, is short in comparison with the length of lineI0.

Single line repeaters 60 may be of any suitable 75 ratus lshown atstation 52. However, the source of power associated with terminalapparatus 88 is usually insufficient to permit loops of several milesbetween the terminal apparatus and the teletypewriter 52.

The terminal apparatus of. repeaters and 84 connected to line 85 is alsoarranged in accordance with the embodiment of this invention shown inFig. 2, which is self-compensating and requires no adjustment in theapparatus at either of these repeaters and repeater stations tocompensate for variations in the leakage resistance of line 85. It is tobe understood that the repeaters or repeater stations 82, 84, 86 and 88are all located along the telegraph line or channel between theinterconnecting station shown in Fig. 7 and the outlying station 52shown in Fig. 8. However, it is to be noted that the equipment connectedtothe ends of line 85 has been reversed. In other words, the end of line85 towards the interconnecting station shown in Fig. 7 is connected toground and positive battery by repeater 86 instead of to positive andnegative battery, while the 'end of line 85 more remote from theinterconnecting station of Fig. 7 is connected to positive and negativesources of potential by the equipment in repeater 84. It is thus obviousthat the equipment at the ends of the long telegraph lines orcomposited, telegraph channels may be inter- Vchangedto that shown anddescribed'in and with reference to Fig. 2. This also applies withrespect to the embodiment of this invention shown in Figi, it' beingobvious that the transmitting and receiving apparatus shown at station Amight be equally well located at station B if the apparatus at station Bwere located at station A. It is also possible to arrange either or boththe systems shown in Figs. 1 and 2 in long lines with either end of anyof the sections toward the central oiiice and the other end away fromthe central oiiice. Thus, it is possible to have a repeater comprisingtwo terminal equipments similar to that shown at station B connectedtogether or two similar to the equipment shown at station A in Figs. 1and 2 connected together, or it is possible to have equipment shown atstation B connected to equipment similar to that shown at station A ofeither Fig. 1 or 2 and either of these embodiments connected to the lineextending towards the central oiiice and the other equipment connectedto a long toll line extending away from the central oice orinterconnecting point.

As shown in Fig. 2 variable resistance 24 isprovided to control thepotential of point 23 and thus make all the controls for insuring thatboth ends of the line will be self-compensating at the central officeend rather than at the outlying end. In case, however, the apparatus attwo ends of -the line are interchanged, in other words, the apparatus atstation B is located at the central or interconnecting point,apotentiometer may be provided between the contacts ofthe sending relay38 and line I 8. This will permit the adjustment of the potentialapplied to this end of the line so that all the adjustments still can bemade at the central point and none at the outlying subscribers telegraphstations.

The repeaters connected to line 81 are similar to those connected toline 85 excepting as pointed out before. The equipment located at theinterconnecting station shown in Fig. 7 connects sources of positive andnegative potential to line 81 whereas the repeater equipment of repeater88 connected to line 81 connects positive potential and ground to theline. vIn other words, the

equipment at the two ends of the line is reversed from that of line 85.

It is to be noted that the system shown in Figs. l and 2 will notoperate as a full duplex telegraph system. That is, signal impulsescannot be transmitted over the line connecting the stations A and B inboth directions at the same time and independently of each other. It isonly possible to transmit these signals over the system in one directionat a time. This is due to the fact that when the source of potential isconnected to the line at station B by the transmitting devices at thisstation, the receiving relays at both stations A and B are positionedindependently of the transmitting device I2 at station A. In Fig. l thereceiving relays I5 and I8 at stations B and A, respectively, arepositioned to their spacing contacts or positions when the transmittingcontacts I I are open, so that sources of potential I6 and 32 areconnected to line I0. The armatures of these relays remain on theirspacing contacts so long as the contacts Il, or any break contacts inseries with them, remain open independently of the position oftransmitting relay I2 at station A. In Fig. 2 the armature of relay I5at station B is positioned to the marking contact while the receivingrelay I8, break relay 34 and vibrating relay 35 at station A assumetheir spacing positions when sending relay 38 connects the source ofpotential 93 to the line. These relays assume these positions andmaintain them during the time the sending relay 38 is connecting batteryto the line independently of the position of the sendingrelay I2 atstation A. It is thus evident that during the time potential isconnected to the line at station B it is impossible to transmit signalsfrom station A to station B. Consequently, it is impossible to operatethese systems on a full duplex basis.

The arrangements shown in Figs. 1 and 2, however, have the advantage,when operated in the so-called half duplex manner of operation in whichsignaling impulses are transmitted in only one direction at a time, thatthe usual number of break relays are not required. This can be mor-efully understood by reference to the more comprehensive system shown inFigs. 6, 7 and 8.

As described above, stations 50 and 5I are connected to a centralinterconnecting point or station by means of the telegraph system shownin Fig. 1.

When it is desired to senda break signal from stations 50 and 5I duringthe time they are receiving signalimpulses from the interconnectingstations shown in Fig. 7, the transmitting device Il at either of thesestations, or a break contact connected directly in series with them, isopen. This connects either source of potential i6 or 55, as the case maybe, to line I8. As pointed out above, under this condition, thereceiving relays i5 at stations 50 and 5I as well as the receiving relayI8 of repeater 51 at the central interconnecting station shown in Fig. 7assume their spacing positions and maintain these spacing positionsindependently of the position of the sending relay 58 of repeater 51.This insures the breaking of the signals received at stations 58 and 5|and also the transmission of a break signal through repeater 51 by thereceiving relay I8 over line SI to the other repeaters and stations oi.the system shown in Figs. 6, 7 and 8.

When it is desired to transmit a break signal from some other station ofthe system to either stations 58 or 5I during the time they aretransmitting telegraph signal impulses to the other stations, a breaksignal will be transmitted from the station desiring to send the breaksignal. Assume that the break signal is transmitted through thesinglelinerepeater 60 of Fig. 7 over the line 6I to repeater 51 andthence over line I to stations 5| and 50. Under this condition, the line6I is opened bythe single line repeater 60 sothat the lower windings ofthe sending relay 58 and the break relay 59 control these relays. Sincethese windings are connected to thereceiving relay I8, these relays willfollow the receiving relay I8. Now, the receiving relay I8 of therepeater 51 will follow the signals transmitted from thetransmittingdevice Ilat stations 58 or 5I independently of the positionof the sending relay 58 of repeater 51 so that relay I8 may continue tofollowthe signal impulses transmitted from stations 50 and 5I. However,under these conditions the break relay 59 connects the same potential toboth contacts of the receiving relay' I8 so it will not cause relays 58and 59 to follow the operation of relay I8, thus insuring that thesending relay 58 remains on its spacing contact and transmits aspacingsignalto stations 58 and I. This spacing signal will interrupt therecording of the home copy fat these stations `and i thus indicate tothe attendant ,that another staover this system.` y

tion wishes to break in and transmita message It is thus evident that abreak relay` is required at onlyone end of theline I0,V namely, the endat which signals are transmitted by connecting potentials of oppositepolarity to the line.

As pointed out above, signal impulses are transmitted from station 49over line 62to repeater 63 by meansof the system shown in Fig. 1. Sincethe other line 64 connected to repeater 63 is provided withanintermediate station 65 which may open the line 64 toztransmit breaksignals tostation -ll9, it is necessary that repeater v63l be alsoprovided with a break rel-ay 12 which operates in a manner similar tothat described with reference to the break relay 59 of repeater 51. Incase line 54 does not include an intermediate telegraph station, thenthe break relay 12 will not be required because the line 64. wouldneverbecome open-circuited. Consequently, both the windings of relays 1Iand 12 would be atall times effective so that the positionof` thearmatures ofthese relays would be independent of the position of thearmature of the receiving relay I8. `Under these conditions no breakrelay would be required because the sending relay 1I would move to itsspacing contact on break signals received from line 64 and remain thereso' long, as the break signalis received by this relay.l It'will,therefore, transmit this break signal to station 49' during the timestation 49 is transmitting the signal impulses and indicate to theoperatorithere that another station of the system may wish tol break inand transmit a message.

Signal impulses are transmitted over the line 61 between repeaters 56and 68 in accordance with the telegraphV system shown in Fig. `2.Whenjit is desired to-transmit a break signal from station 49 orstation6:5 whichA is connected to repeater 66 by means of line 64 during' thetime theV signal impulses are being received at these stations' fromanother station connected` to the telegraph system shown in Figs. 6, 7and 8,

line 56 may be open at station 65. This causes the sending relay 10 ofrepeater 61 to move toits spacing contacts during thev next marking.signal impulse received by receiving relay94 from line 61.` This will.maintain relay 94 in its marking the transmitting station indicating tothe trans-YV mitting operator or attendant that station 65` wishes tointerrupt the transmission of signals andtransmit to the other stationsof the system.

vIn case it is desired to'transmita break signal from some other stationof the system to station 55 during the time station 65istransmittingsignal impulses, the break signal will be transmitted fromthese stations' through repeater 58. Assume that the break signalisltransmitted through single line repeater 60 which will open line 69totransmit a break signal to repeater 68. This interrupts the circuit ofthe upper or line windings of the Ysending relay 96 and the break relay91 of repeater 68. This means that these relayswill beoperated bytheirlower windings from the received. relay 95 which will followthesignal impulses-'transmitted from stationV 65. To prevent sendingrelay 96 from following these signals and interfering with the breaksignal it (relay 96) Vline 61 `after the break signal is received overline 69. This insures'that both thersend andbreak relays 96 and 91thereafter remain on their spacing contacts and transmit a spacing orbreak signal to station {i5-through repeater 66. It is thus evident thatin the'arrangement shownV in Fig. 2"as in-the system'shown in Fig. l, abreak relay is required only at the end of the line that positive andnegative sources of potential are used to transmit the signal impulsesover the line.

The same break arrangement is also shown in the repeaters 13 and 14connectedto the ends of line 15'. Repeater 13` connects sources of bothpositive and negative potential to line 15 to transmit signal impulsesto repeater 14. Consequen'tlya break relay 98 is required at thisrepeater.Y Repeater 14, however, transmits impulses .of one polarity andground over line 15. Consequently, no break relay is required andnone isprovided.

As pointed out above with reference to line 84, no break relays areprovided for repeater 84 of Fig..8" because repeater 84 of Fig. 8 is athrough repeater andthe line.85 connected thereto does not come to anintermediate station, so that this line is neveropen.` Thus, both theline and balancing.V windings of relay 99 to repeater 8d are alwayseffective to control this relay. Consequently, the position of thearmature of this relay isindependent of the position of the receiving'relay' |90 of this repeater, sothat break signals willbe transmittedthrough repeater 84 in both directions without the use of break relays.

TheY telegraph station 52 is connected to repeater'82- by means of twoloops, one loop being used to transmit signal impulses and the otherloop" being used to receive signal impulses at station 52. In this casedue to the divided loop between station 52 and repeater 82, it isnecessary to makesome provisionsin repeater 82 to insure theprope'rtransmission of break signals to and from station 52. The transmissionof break signals from'station 52 duringthe reception of signal impulsesthereby is similar to the transmission of break signalsV from station 53in that the receiving ,relay 38 of repeater 82 is operated to itsspacing position. This connects a source of potential IIlI to the line83 which causes receiving relay I5 to be maintained in its markingposition, thus insuring the transmission of the break signalindependently of the reception of signals from line 83.

However, in case it is desired to transmit a break signal to station 52during the time signal impulses are being transmitted from station 52,some means must be provided to prevent the sending relay 38 of repeater82 from operating the receiving relay to its marking position during thetime the receiving relay I5 is in its spacing position. If suchadditional means are not provided, the operation of relays 38 and I5 asdescribed will interfere with the transmission of the spacing or breaksignal from relay I5 to station 52. As shownin repeater 82 the spacingcontact of relay I5 is connected to the upper or line winding of thereceiving relay 38. This causes relay 38 to lock in its marking positionwhen relay I5 has been operated to its spacing position by the receptionof the break signal as soon as relay 38 is operated by a marking signaltransmitted irom station 52. This insures the proper transmission of thebreak signal received over line 83 to station 52 because relay 38 islocked operated so relay I5 will be maintained in its spacing positionso long as the break signal is received over line 83 and will transmitthe signal to this station 52 independently of the operation of thetransmitting device II at station 52.

In case the received signal impulses` are transmitted over the receivingloop of the split or divided loop by means of polar signals, that is,

the signal impulses of positive and negative polarity, both contacts ofthe receiving relay I5 are required to transmit these signal impulses.Consequently, the spacing contact is not available to lock thetransmitting relay 38 in its operated position during the time the breaksignal is received and thus insure the proper transmission of the breaksignal to the telegraph station or apparatus. In this case, as shown inFig. 2, an additional break relay 4I is required. This relay isconnected in series with the spacing contact of the receiving relay andconnects ground in parallel with the transmitting contacts or device IIat station B, thus insuring the proper transmission of a break signalfrom receiving relay I5 to the receiving apparatus at thestation duringthe time signal impulses are being transmitted by the transmittingdevice II because the operation of transmitting device II at thisY timecannot cause relay 38 to repeat the signal impulses transmitted thereby.

It should be noted that the receiving relay I5 at station B- of Fig. lcorrectly responds to both the signal impulses received from station Aand to the signal impulses transmitted from station B so that thereceiving magnet of the printing or recording device 30, when connecteddirectly to the contacts of this receiving relay I5, will record bothsignal impulses received from station A and the impulses from station B,which is usually called the home copy.

However, the receiving relay I5 of station B of the system shown in Fig.2 responds only to the signal impulses transmitted to station B fromstation A but does not respond to the signal impulses transmitted fromstation B. Consequently other provisions must be made for the recordingof the home copy at station B. As shown in Fig. 2, the circuit of theprinting magnet 30 of the receiving or recording'device at'thisstationis connected in series with the transmit- -ting contacts of relay38, so that it will also receive the signal impulses transmitted by thetransmitting relay 38 from station B.

.This is also true of the circuit of magnet 3U at station 52 which isconnected to the transmitting contacts of the sending relay 38 so thatit will receivezthe same impulses as are transmitted from station 52 andthus provide a home copy of the ymessages transmitted from station 52.In the case of station 53 the receiving magnet is connected directly inseries with the transmitting contacts II so that it will follow all thesignal impulses transmitted by these contacts. In this arrangement nospecial provision is, therefore, necessary.

The term source of potential as used in this specication and, inparticular, in the appended claims includes sources of zero potential,i. e., ground potential, as well as sources of both positive andnegative potentials.

What is claimed is:

l. A telegraph communication system comprising a first station, a secondstation, a direct current telegraph line connecting said stations,terminal composite circuitsr included in said line, intermediatecomposite sets included in said line, an open-Wire portionsubject tovarying leakage conditions included in said line, receiving means ateach of said stations, transmitting means at each of said stationsconnected to the ends of said line for transmitting two signalingconditions to the other of said stations the values of which are soirelated to each other and to said line that the algebraic sum of thecurrents of said signaling conditions at the other of said stations issubstantially independent of variations of the leakage resistance ofsaid telegraph line, said transmitting means being arranged to havesubstantially the same impedance when transmitting both of saidconditions to the opposite station, and variable biasing means at one ofsaid telegraph stations for adjusting the receiving means thereat torespond equally to said two conditions transmitted thereto from theother of said stations.

2. Atelegraph system comprising a rst station, a second station, adirect current telegraph signaling channel connected between saidstations, transmitting means at said first station for connectingsources of potential of substantially equal magnitude but oppositepolarities to said telegraph channel, transmitting means at said secondstation for normally connecting ground to said telegraph channel and forconnecting a source of potential to said channel in accordance Withsignal impulses to be transmitted thereby which is so related to saidother sources of potential and to said channel that the algebraic sum ofthe currents received at said iirst station is independent of variationsof the leakage resistance of said telegraph channel, receiving apparatusat said second station for responding to the sources of potential ofopposite polarities connected to said channel at said rst stationwhereby the algebraic sum of the signaling conditions received at saidsecond station is independent of variations of leakage of said telegraphchannel, receiving apparatus connected at said first station,`variablebiasing means connected to said receiving apparatus at said firststation for biasing said receiving apparatus to respond equally to bothsignaling conditions connected to said channel at said second station.

3. A telegraph system comprising a first station, a second station, adirect current telegraph communication channel connecting said stations,receiving apparatus connected to said channel at each of said stations,transmittingapparatus at said rst station for normally connecting asource of potential to said channel and transmitting apparatus at saidsecond station for normally connecting ground to said channel,additional means connected to said transmitter at said rst station forconnecting to said transmission channel in accordance with the signalsto beitransmitted a source of substantially equal magnitude, but ofopposite polarity to the source of potential normally connected to saidtransmission channel at said lrst station, and additional means at saidsecond station for connecting a source of potential to said transmissionchannel in accordance with the signals to be transmitted of such a valuethat the current normally flowing over said line is increased, saidsources 4of potential being so related to each other and saidtransmission line that the algebraic sum of the `signaling currentsreceived at each of said sta-` tions from the other of said stationsisgsubstantially independent of the leakage of said line.

4. A telegraph system comprising arfirst station, a second station, adirect current telegraph channel connecting said stations, said channelincluding terminal and intermediate composite sets and a portion ofopen-wire line subject to varying leakage, means for transmitting andreceiving two diierent signal conditions to and from each of saidstations, resistance means connected in said line cooperating with thetransmitting means at each .of said stations for rendering the algebraicsum of the signaling currents received at each of said stati-onssubstantially independent of said varying leakage, and biasing meansassociated with said receiving means at each of said stations forproducing a biasing eiiect upon saidrreceiving means which issubstantially one-half Vthe effect of the algebraic average of saidreceived signaling currents but opposite in direction thereto.

5. A telegraph system in which the receiving apparatus responds equallywell to all signaling impulses for any given value of leakage resistancecomprisinga telegraph line subject to varying weather conditions, meansfor normally transmitting current over said line, means/fortransmittingv signal impulses of opposite polarities over said lineconnected to one end of said line, means for transmitting signalimpulses of current substantially three times the magnitude of saidnormal current from the other end of said line, and receiving apparatusconnected to each end of said line which is responsive to the signalimpulses transmitted from Vthe other end of said over and means foradjusting the magnitude ofV said sources of potential so that the ratioof substantially twice said rst potential to said second potential, isequal to the ratio of the `resistance of said line measured from saidfirst end to the point where an equivalent concentrated leakageresistance would be connected to the line to the remainder of theresistance of said line.

'7. A telegraph system comprising a telegraph line, transmitting andreceiving apparatus connected to each end of said line, sources ofpositive and negative potential connected to the transmitting apparatusat. one-end of said line,

ground'and a source of one potential connected to the transmittingapparatus at the other'end of said line and potentiometer meansconnected between the transmitting apparatus at the iirst end of saidline and said line for so adjustingthe relative potentials connected tothe ends of said line that the sum of the currents received at each endof theline is substantially constant and independent of the leakageresistance of the line.

8. A two-way self-compensating telegraph system comprising a rststation, a second station, a telegraph line connected between saidstations, means for normally connecting a source of potential to one endof said line and for connecting ground to the other end of said line,means for transmitting signal impulses of opposite polarity connected tothe iirst end of said line, and means for transmitting signal impulsesof increased magnitude from the other end of said line, receiving meansconnected tof each end of said line for receiving impulses transmittedfrom the opposite end of said line, and variable bias means connected tothe receiving apparatus at said first end of said line, and meansconnected to said line for controlling the relative magnitudes of saidimpulses so that the algebraic sum of impulses of different character issubstantially constant and independent of the leakage resistance of theline.V

9. A telegraph system in accordance with claim 8 characterized in thisthat a potentiometer is connected between the transmitting means at saidrst end of said line and said line for adjusting the relative magnitudesof said impulses of different character, whereby all of the adjustmentsofthe relative magnitudes of said impulses by which the .algebraic sumof the received impulses is made independent of the leakage of saidline, may be made at said rirst end of said line. 10. Aself-compensating telegraph system comprising a rst'telegraph station, asecond telegraph station, means for normally transmitting a current oversaid line, meansrfor transmitting signal impulses of opposite polarityin o-ne direction over saidf line and signal impulses of increasedmagnitude in opposite direction over said line, the receiving meansconnected to each end of said line for receiving the impulsestransmitted from the opposite end of said line, and means for adjustingsaid receiving apparatus and the magnitude of said impulses so that thebias of the received impulsesis substantially independent of the leakageof said line.

11. A two-way telegraph system comprising a first station, a secondstation, adirect current telegraph channel connected between saidstations, means for transmitting two signal conditions of oppositepolarity from said rst station to saidl second station, means fortransmitting two signaling conditions of different magnitude from4 saidsecond station to said first station, receiving apparatus at each ofsaid stations connected to said line for receiving the signal conditionstransmitted from the other of said stations, and means for adjustingsaid receiving apparatus and the relative 'magnitudes of all saidsignaling conditions so that one of said signaling conditions at each ofsaid stations increases as much as the other of said signalingconditions decreases with a change of the leakage of said line.

12. In a two-way telegraph system, a rst station, a second station,means for transmitting signal impulses from each of said stations to theother of said stations, means at each of said stations for receivingimpulses transmitted to it from .the other of said stations, means forso adjusting the bias of said receiving apparatus and means for soadjusting the magnitude of the signaling impulses that the eiective biasof said receiving apparatus is automatically varied with changes of theleakage of said line to maintain the quality of the received signalssubstantially constant.

13. A telegraph system comprising a line, a portion of which issubjected to variable leakage resistance, receiving apparatus connectedto each end of said line, apparatus for transmitting two diierentsignaling currents from each end of said line the sum of which asreceived at the opposite end of the line is substantially constant andindependent of said line leakage resistance and biasing means connectedto said receiving apparatus which produces an eiect opposite to andsubstantially equal to one-half the magnetic effect of the sum of thesignaling currents received by said receiving apparatus.

14. A method of operating a telegraph system in which two signalingcurrents are transmitted in each direction thereover which comprisesadjusting the magnitude of the two currents received at each end of theline so that their sum is substantially constant and independent of theleakage resistance of said system and adjusting the bias of thereceiving apparatus at each end of the system so that its magneticeffect is opposite to and equal in magnitude to substantially one-halfthe magnetic eiect of the sum of the two signaling currents receivedthereby.

15. A signaling system comprising a line, a portion of which issubjected to a variable leakage resistance, transmitting apparatusconnected to each end of said line for transmitting two signalingconditions thereover the sum of the currents of which, as received atthe opposite end, is substantially constant and independent of the valueof said variable leakage resistance, receiving apparatus also connectedto each end of said line, and biasing means connected to said receivingapparatus which produces a magnetic effect thereupon opposite tosubstantially onehalf the magnetic effect of the sum of said currentsreceived thereby.

16. The method of operating a telegraph system in which two signalingconditions are transmitted over a telegraph line in each direction whichcomprises adjusting transmitting potentials at both ends of the line sothat the sum of the currents received at each end of the line for bothsignaling conditions remains substantially independent of the value ofthe leakage resistance of the line and adjusting the receiving apparatusat each end of the line to respond equally to both signaling conditionsreceived thereby.

17. The method of operating a telegraph system a portion of which issubjected to a variable leakage resistance and in which two signalingconditions are transmitted in each) direction' thereover which comprisesadjusting the transmitting potentials at each end of the system so thatsubstantially the same magnitude of current leaks o through the leakageresistance for each of the signaling conditions transmitted over thesystem in each direction and adjusting the rcceiving apparatus connectedto the system to respond equally to the two signaling conditionsreceived thereby.

18. The method of operating a telegraph system a portion of which issubjected to a variable leakage resistance in which two signalingconditions are transmitted in each direction thereover which comprisesadjusting the transmitting potentials at each end of the line so thatpotentials of substantially the same magnitude appear across theeffective leakage resistance for 'both the signaling conditionstransmitted in each direction over the system and adjusting thereceiving apparatus to respond equally to the signaling conditionstransmitted from the opposite end of the system.

19. The method of operating a telegraph line a portion of which issubjected to a variable leakage resistance which comprises applyingthree signaling conditions thereto, adjusting the potentials for causingsaid signaling conditions so that the potential across the eiectiveleakage resistance of said line is of substantially the same magnitudefor all of said signaling conditions.

20. An impulse transmitting system comprising a line, impulse receivingapparatus connected to each end of said line, impulse transmittingapparatus connected to each end of said line having two positions, meanseffective when said transmitting apparatus connected to one end of saidline is in either of said positions for connecting to said line sourcesof potential which are so related to each other and to the electricalcharacteristics of said line that the bias or the impulses transmittedin one direction over said line is substantially constant andindependent of the leakage resistance of said line, means eiective whensaid transmitting apparatus connected to the other end of said line isin either of said positions for connecting to said line sources ofpotential which are so related to each other and to the electricalcharacteristics of said line that the bias of the impulses transmittedin the other direction over said line is substantially constant andindependent of the leakage resistance of said line.

21. An impulse transmitting system comprising a line, impulse receivingapparatus connected to each end of said line, impulse transmittingapparatus connected to each end of said line having two positions, meansfor connecting sources of potential to said line when said transmittingapparatus are in their respective positions for causing impulse currentsto flow thereover, which potentials are so related to each other and tothe electrical characteristics of said line that the algebraic sum ofthe impulse currents received at either station from the other stationis substantially constant and independent of the leakage resistance ofsaid line.

22. An impulse transmitting system comprising aline, impulse receivingapparatus connected to each end of said line, impulse transmittingapparatus connected to each end of said line having two positions, meansfor connecting sources of potential to said line when said transmittingapparatus are in their various positions, which sources of potential areso related to each other and'to the electrical characteristics of saidsignaling conditions transmitted from either end of said line is thesame.

23. An impulse transmitting system comprising a line, impulse receivingapparatus connected to each end of said line, impulse transmittingapparatus connected to one end of said line for transmitting twodifferent impulse currents over` said line, means for so establishingthe polarities and magnitudes of said currents with respect to eachother and the electricalcharacteristics of said line that their sum asreceived at the opposite end of said line is substantially constant andindependent of the leakage resistance of said line, impulse transmittingapparatus connected tothe other end of said line for transmitting twodifferent impulse currents over said line, means for so establishing thepolarities and magnitudes' of said currents with respect to each otherand the electrical characteristics of said line that their sum asreceived at the opposite end of said line is substantially constant andindependent of the leakage resistance ofsaid line.

24. An impulse transmitting system comprising a line, impulse receivingapparatus connected to each endof said line', impulse transmittingapparatus connected to each end of said line for transmitting twodifferent impulse currents over said line, means forso establishing thepolarities and magnitudes of said currents with respect to each otherand to the electrical characteristics of said line that the bias of saidimpulses as received at the opposite end of the line is substantiallyconstant and independent of the leakage resistance of said line.

25. An impulse transmitting system comprising a line, impulse receivingapparatus connected to each end of said line, impulse transmittingapparatus connected to each end -of said line for transmitting twodifferent impulse currents over said line, means forso establishing thepolarities and magnitudes of said currents with respect to each otherand to the electrical characteristics of said line that said impulses asreceived at either end of said line differ by the same amount from anaverage value for any given value of leakage resistance` of said line.

26. An impulse transmitting system comprising a rst station, a Isecondstation, `an impulse transmitting channel connected between saidstations, impulse transmitting apparatus connected to said channel atone of said stations for transmitting impulsesof .two differentmagnitudes over said channel, the magnitudes of which are so related toeach other and to the electrical characteristics conditions transmittedof said channel that their sum remains substantially constant andindependent of the leakage resistance of said channel and receivingapparatus connected to said channel `at said second station forresponding to said impulses.

27. An impulse transmitting system comprising a first station, a secondstation, an impulse transmitting channel connected between saidstations, impulse transmitting apparatus having two p0- sitionsconnected to said channel at one of said stations for transmittingimpulses of two diilferent magnitudes over said channel, impulsereceiving means connected to said channel, means for connecting a sourceof potential to said channel at said second station and means forconnecting sources of potential to said` channel when said transmittingapparatus is in either of said positions, which potentials are sorelated to each other and to the electrical characteristics of saidchannel that the sum of the currents received at said second station issubstantially constant and independent of the leakage resistance of saidchannel.

28. A telegraph system comprising a telegraph line, means at each end ofsaid line for impressing upon the line two signaling conditions, abiased receiving instrumentality at each end of the line to respond tosaid two signaling conditions trans- Vmitted from the other end, meanseffective with any leakage current between zero and a large valuewhereby one of said vsignaling conditions transmitted at either distantend of said line adds an eiTect of a certain magnitude to the biasedcondition of said receiving apparatus, and means effective with the sameline leakage current whereby the other condition subtracts an effect ofequal magnitude therefrom.

29. A telegraph system comprising a telegraph channel of a compositetoll line subjected to variable leakage resistance conditions, receivingapparatus connected toI each end of said line, means for applying twosignaling conditions to each end of said line, potential means connectedto said transmitting apparatus so related to each lother and to thedistribution of the line resistance and leakage resistance that themagnitude of potential across the equivalent concentrated leakageresistance of any given value is substantially the same for all thesignaling conditions b-ut of opposite polarity for the two signalingfrom either end of the line. l

WALTER W.` CRAMER.

